Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
309 PM CDT Sat Apr 19 2014
Tonight and Sunday..forecast confidence medium.
A vigorous shortwave moving along the Canada/ND/MN borders is
allowing for warm and moist air to flow into southern WI this
weekend. Precipitable water values rise to 1 inch along the
associated surface trough/cold front with that compact system to our
north. That frontal boundary will stall over central/northern
Wisconsin tonight. 925-700mb frontogenesis and a series of 500mb
shortwaves and resultant rising motion will be the focus for
numerous showers and a few rumbles of thunder to develop there. I am
hanging on to a small chance for shower development in the far
northern mkx forecast area based on the 12z European model (ecmwf)... WRF-arw and WRF-
nmm model quantitative precipitation forecast...but it seems unlikely.
850mb temperatures will be on the rise across southern WI all day Sunday as
a 500mb trough digs into the Central Plains. The shortwave with this
upper trough will gradually lift into northern Illinois/southern WI Sunday
night and Monday...but the steady warm air advection ahead of it will reinforce
that stalled frontal boundary over central WI during the day Sunday.
Thus...stalled the southward progression of probability of precipitation into Madison or
Milwaukee until very late in the afternoon. It is possible we will
hear some rumbles of thunder- there is a little elevated cape
available...along with decent Omega.
Southeasterly winds will become southerly overnight...then take on
more of a southwesterly direction Sunday afternoon. This will allow
temperatures to warm up into the 60s near the lake for a change.
Inland temperatures are expected to warm into the lower 70s south and upper
60s north. There is uncertainty about how quickly the thicker 5000-
foot and middle level clouds will overspread southern WI Sunday
Sunday night and Monday...forecast confidence medium.
A decent middle/upper level trough will be located over the Central
Plains Sunday night...moving across the area on Monday. The
surface boundary will hold stationary along or just north of our
northern forecast area border Sunday night...from about Green Bay
to La Crosse. This should help to keep the bulk of the precipitation
north of mke/msn through Sunday night...maybe squeaking into far
southern areas toward sunrise on Monday. On Monday...the upper
level trough will arrive...along with it/S associated surface
circulation. This will finally help to enhance or increase precipitation
chances across the entire forecast area on Monday. We should see a
trend toward decreasing precipitation chances during the late morning or
early afternoon west of Madison and during the late afternoon in
the far southeast. The airmass will remain very mild...so despite
the rain/clouds...temperatures will stay mild with highs in the 60s...to
around 70 along the border with Illinois.
Monday night through Tuesday night...forecast confidence is high.
The last of any lingering precipitation will exit the southeast Monday
evening. High pressure will then slide across the area during this
period...with the ridge axis over Lake Michigan at 12z Wednesday.
Fairly strong cold advection kicks in on Tuesday with highs a
good 10 to 12 degrees colder than Monday. Winds will likely shift
to onshore along Lake Michigan during the afternoon...so extra
chilly there. Also expect a bit more cloudiness as well in the
Wednesday through Friday...forecast confidence is medium.
We will evolve from a large scale upper ridge pattern over the
Great Lakes early in the period to a large upper level trough
moving through by Friday. As the lower tropospheric ridge slides
east early on Wednesday...we/ll see a strong warm advection surge
move into the area by afternoon and could result in some showers
or even a thunderstorm for areas roughly west of Madison.
Cyclogenesis will be ongoing over the plains Wednesday night and
this Marks a shift into a more active and moist southwest middle
level flow through Thursday night for the western Great Lakes. The
upper trough/low will then move through on Friday. It/S tough to
add specific timing to precipitation trends at this point...but it looks
unsettled until the surface low moves through later Thursday night
into Friday. The European model (ecmwf)/GFS/Canadian are in reasonable agreement
with the speed of the system...with the ec on the faster side.
VFR conditions forecast through at least Sunday afternoon at taf
sites. Moisture will increase on Sunday but with only small
chances of showers in the afternoon north of Madison and
Milwaukee. The best chance for afternoon rain showers and the
possible resultant MVFR ceilings/visibilities will be along and north of a
dll to fld to sbm line. The rain will likely hold off until after
12z Monday at all the taf sites.
Marine...south winds of 10 to 15 knots are expected tonight which
will allow waves to approach 4 feet in the nearshore waters of
Sheboygan County late tonight and sun am. A Small Craft Advisory is
not anticipated at this time but boaters should remain aware of the
marine conditions and forecast.
Tonight/Sunday and aviation/marine...mrc
Sunday night through Saturday...Davis